A walk-behind working machine with a front wheel disposed in front of a rotary working portion is disclosed, for example, in Japanese Patent Laid-Open Publication No. HEI-10-225202. This walk-behind working machine will be described with reference to FIG. 10 hereof.
A walk-behind working machine 201 in the related art shown in FIG. 10 includes a drive case 203 (including a transmission case 204 and a rotary case 205) disposed at the lower part of a machine body 202, a rotary shaft 206 of a rotary device provided at the rotary case 205, a wheel support arm 208 mounted to right and left plates of the machine body 202 by a pivot 207, a front liftable wheel 209 mounted to the distal end of the wheel support arm 208, and a lifting and lowering adjustment lever 211 connected to the wheel support arm 208. The height of the front liftable wheel 209 is adjusted by operating the lifting and lowering adjustment lever 211.
This walk-behind working machine 201, however, has a possibility that when a large load is applied to the wheel support arm 208, the right and left plates supporting the wheel support arm 208 can be deformed. It is desirable especially for large-size farm working machines that a support structure of a wheel support arm be increased in strength without losing the lightness, that is, a support device for supporting a front wheel be strengthened.